Dental prostheses comprising a dental implant (also referred to as an anchoring part) inserted in the jaw and an abutment (also referred to as a body part or secondary part) fastened thereon are known sufficiently as a denture, wherein these two parts can also be formed as a unit (that is to say in one part and integrally). The abutment, which is preferably produced from metal or ceramics, wherein plastic or polymer compounds are also possible, is connected with a non-positive or positive fit to the dental implant by means of a screw. The screw is preferably produced from titanium, wherein embodiments made of steel are also possible however.
The prosthesis matched to the tooth profile is generally inserted as soon as the implant inserted in the patient's bone has healed, this insertion process being carried out by the treating doctor. A dental laboratory supplies the prosthesis components necessary for this, which are composed of the abutment with the tooth crown or bridge fabricated individually thereon and a (connecting) screw. To fix the abutment to the dental implant, the abutment is fitted on the implant; a connecting screw is then introduced through a bore in the abutment and is then screwed into an inner thread of the dental implant. The abutment and the dental implant are thus interconnected with a positive fit. The screw is generally tightened with a torque of more than 30 Nm, generally with a torque of approximately 35 Nm. Due to the confined spatial conditions in the mouth and as a result of the dimensions of the dental prosthesis, such connecting screws have to be relatively small so that they fit in the tooth crown.
A connecting screw within the meaning of the present invention can not only be used to fasten an abutment to a dental implant, but also to fasten a tooth crown to an abutment, a meso-abutment or a (one-part) dental implant.
A connecting screw of this type is known for example from DE 20 2008 003 187 U1. The connecting screw can also be formed in two parts, as disclosed in EP 1 972 297 A1 for example.
Such connecting screws typically have a shaft portion and a head portion. The shaft portion normally has a smaller diameter than the head portion and has an outer thread, which is screwed into the inner thread of the dental implant or abutment, whereas the head portion, when connected, rests on an inner shoulder in the bore in the abutment or the crown. In addition, an engagement means for a rotary tool is normally formed integrally on the head portion so that a sufficient torque can be transferred to the screw with the aid of a rotary tool.
This engagement means can be formed for example as an external or internal hexagon or as an external or internal torx, also referred to as a hexalobular external or internal driving feature. Standard EN DIN ISO 10664 describes a corresponding internal torx for screws and is hereby incorporated by reference.
The rotary tool comprises counter means corresponding to the engagement means of the screw. Rotary tools suitable for transferring a torque to a screw with an internal torx are likewise specified in standard EN DIN ISO 10664 for example and are hereby incorporated by reference.
An alternative embodiment of screw head and rotary tool is disclosed for example in DE 10 2004 026 769 A1.
One difficulty when anchoring the connecting screw in the dental implant is that a longitudinal axis of the bore in the abutment or the crown might not lie precisely in the extension of a longitudinal axis of the inner thread or of the dental implant, and instead these longitudinal axes are arranged at a certain angle to one another. A similar situation occurs if the bore inside the abutment or the tooth crown is angled. As a result of such an embodiment of the bore, the discharge opening of the bore may be placed in the tooth crown in such a way that it is not normally visible from the outside, that is to say the discharge opening can be arranged on the lingual or palatal side of the crown. However, it may also be necessary, due to the anatomical preconditions in a specific patient, for the bore to be angled or for the bore in the crown and the cavity in the implant to be arranged at an angle to one another.
In both cases, not only is it difficult to introduce the connecting screw through the bore in the abutment or crown into the inner thread of the dental implant, but it is also difficult in particular to tighten the screw with the aid of a rotary tool: such a rotary tool not only has to be brought into engagement through the bore with the engagement means on the connecting screw, but must also cooperate with said connecting screw in such a way that a torque sufficient to provide a reliable fastening can be transferred. To this end, the engagement means on the screw and the counter means on the rotary tool have to be matched to one another as precisely as possible so that the tool does not have too much play and the engagement means are not damaged.
The object of the present invention is therefore to allow a rotary tool to be introduced and a connecting screw to be tightened, even if the longitudinal axis of the bore in the abutment or the tooth crown and the longitudinal axis of the inner thread of the dental implant are arranged at an angle, in particular at an acute angle, to one another or if the bore is angled, that is to say if the rotary tool cannot be introduced into the screw in the extension of the central longitudinal axis thereof.
A similar object is achieved for example by WO 2008/024062 A2, in which a tooth crown has an angled cavity. A specific screwdriver having a flexible shaft is used to screw this tooth crown securely to an implant. This shaft may be formed for example by a plurality of interconnected wires or by a flexible core, for example made of plastic or polymer, surrounded by wires. This screwdriver disclosed in WO 2008/024062 A2 can bend in the region of the shaft and can thus adapt to the angled cavity in the tooth crown.
WO 2008/116834 A1 also discloses a specific screwdriver, which allows a screw to be tightened in an angled cavity. This screwdriver has a tip with a substantially rounded cross-section in the axial plane and a substantially polygonal cross-section in the radial plane. In addition, the polygon has at least two sides of different length so as to improve the transfer of a torque to a connecting screw, wherein the connecting screw must have a correspondingly shaped engagement depression, into which the screwdriver according to WO 2008/116834 A1 can be introduced.
In the prior art, the above-described object is thus achieved by using a specifically shaped screwdriver, wherein the screw may have to be adapted accordingly.